This is the library of the National Palace in Mafra, Portugal. It's a beautiful building constructed by and for the now abolished Kings of Portugal. The palace has a library that would make any booklover quiver in joy. The volumes are well-preserved, in part due to the resident bats.

Yes, bats.

The staff permits bats to live in the library. They come out at night and feed on book-eating bugs. Kevin Hartnett writes in The Boston Globe:

In a new book, "The Library: A World History," author James Campbell and photographer Will Pryce survey the world's libraries, from the expansive new National Library of China to the Tripitaka Koreana, which was built in 1251 in South Korea and is one of the oldest intact libraries in the world. The book is full of interesting asides, including the fact about the bats, which live at the Biblioteca Joanina and the Mafra Palace Library in Portugal. In an email, Campbell explained that the bats, which are less than inch long, roost during the day behind "elaborate rococo bookcases" and come out at night to hunt insects which otherwise would feast on the libraries' books. The price of this natural insect control is paid in scat: The bats, Campbell writes, "leave a thin layer of droppings over everything. So each morning the floors have to be thoroughly cleaned...and the furniture has to be covered at night."